This invention is related to a coating composition and in particular to a coating composition that is useful as a formable finish for composite structures made via several different processes.
Many exterior auto and truck parts such as fenders, quarter panels, doors, trim parts, bumpers, fender extensions and other exterior parts are formed of moldable plastic or polymeric materials such as thermoplastic polymers or reinforced polymeric materials. These parts are currently being used because of their corrosion resistance, resistance to permanent deformation on impact and are lighter than metal parts which they replace. Typical moldable thermoplastic polymers that are being use for these parts and that can be easily and economically molded are, for example, polypropylene, polyethylene, ABS (acrylonitrile-butadiene-styrene polymers), polystyrene, and styrene-acrylonitrile copolymers. The lighter weight of these parts favorably affects the weight and fuel economy of the auto or truck made with these parts. Because of these advantages, these plastic parts are replacing metal parts of automobiles and trucks. Another advantage of the moldable polymers is that more intricate designs can be made in comparison to sheet metals giving the auto makers increased freedom in design of autos.
To reduce air pollution, automobile and truck manufactures need to reduce the amount of painting in the manufacturing process. It would be desirable to have a plastic auto or truck part that has a high quality durable and weatherable finish whose color matches any painted sheet metal used to make the auto or truck and that can be attached directly in the assembly process and does not require further priming or painting. This would eliminate the costly and time consuming painting process with the associated pollution problems.
Plastic automobile and truck parts can be made and finished by a lamination coating process, in-mold coating of a part while it is being formed or by a shrink wrap process in which a coated plastic film is shrink-wrapped about a plastic part. A typical shrink wrap process is shown in Mentzer et al U.S. Pat. No. 4,838,973 issued Jun. 13, 1989. Any finish used in the aforementioned processes would have to withstand the processing conditions including heat and deformation and still form a finish useful for the exterior of automobiles and trucks. Attempts have been made to use and reformulate conventional exterior acrylic lacquers and thermosetting acrylic enamels that traditionally have been used on plastic substrates but without success since process conditions used in the aforementioned processes are too severe and adversely affect the resulting finish by causing cracks, distortions and degradation of the finish.
It is an objective of this invention to provide a practical and economical coating composition that can be used in a variety of processes used for decorating plastic substrates that forms a finish that can be thermoformed and molded and results in a finish having an excellent overall appearance, is durable and weatherable and is a useful exterior finish for automobiles and trucks.